The dispersant chemicals used deep below the surface of the Gulf of Mexico to turn oil spewing from the BP Macondo oil well into tiny droplets survived for longer than two months within a deepwater plume of hydrocarbon remnants of the spill after the well was capped, according to a study published in online edition of Environment, Science & Technology magazine.

BP PLC via The Associated PressAn image from video made available by BP shows dispersant being applied to an oil leak during efforts to cap the Deepwater Horizon oil well in the Gulf of Mexico in June. The white wand in the center is releasing the dispersant.

The study indicates that sea life traveling through the deepwater plume likely encountered measurable concentrations of Corexit 9500A, the dispersant used at the wellhead, or of the potentially toxic chemical dioctyl sodium sulfosuccinate, or DOSS, a surfactant contained in the dispersant.

DOSS made up about 10 percent of the estimated 771,000 gallons of dispersant, by weight, that were sprayed into the crude oil and natural gas spewing from the well about a mile below the surface of the Gulf of Mexico, according to the study.

As with a number of research papers based on sampling done during cruises after the catastrophic Deepwater Horizon accident, this one provides only a tiny slice of information that could eventually be used to understand the effects of the spill on marine life and human health, said Woods Hole Oceanographic Institute marine scientist Elizabeth Kujawinski, lead author for the paper.

"The first conclusion is that the molecules that we were studying ended up in the same depth horizon as the deepwater plume that others had observed," she said. "What's important about that is that we don't find it in shallower or deeper water, so somehow it remained associated with the oil plume in some way.

"And what that means is that the dispersants did not contaminate the entire ocean, but only a small portion in a very limited location," she said.

At the same time, the study found that scientists could track the dispersant over a two-month period as it drifted in the plume over a 200-mile path southwest from the well.

"The study shows us where the dispersant ended up and tells us what amount of dispersant was distributed over space and time," said David Valentine, a professor of microbial geochemistry at the University of California at Santa Barbara and co-author of the study. "You can't understand the effects if you don't know how much and how long its there."

The sampling also showed that the smaller and smaller amounts of DOSS found over the two months and farther away from the well resulted from dilution -- the chemical mixing with water -- and not from biodegradation. That stands in contrast to public statements by BP and Corexit officials, who have said the dispersant rapidly biodegrades, in many cases in a matter of days.

The dilution finding also differs from a similar study of methane gas contained in the same plume that found that tiny organisms ate most of it within the same two-month period following the capping of the well in July.

The study is based on samples taken by scientists from Woods Hole Oceanographic Institute in Rhode Island, University of California at Santa Barbara and Stanford University during three cruises in May, July and September.

The scientists found measurable concentrations of DOSS in a water layer traveling about in the Gulf between 6/10ths of a mile and 3/4ths of a mile below the surface. That's the same layer where hydrocarbons had been measured that were the remains of oil droplets and methane gas released from the well.

The study does not come to any conclusions about the potential toxicity of the dispersant and its constituents to marine life, although it points out that deepwater marine life likely encountered the material while swimming through the plume.

"We do know that the highest concentrations we observed are a thousand times less than generally thought toxic," Kujawinski said. But other scientists are expected to use the findings of this study as one factor in determining what might have happened to specific organisms exposed to both the dispersants and the oil and gas from the well, as part of the federal Natural Resource Damage Assessment process.

Additional research also might be needed to determine whether the use of dispersants in deep water is the best alternative for reducing the effects of oil and natural gas released during future accidents, the study said.